Optical imaging apparatus for diagnosis and image processing method

ABSTRACT

An optical imaging apparatus for diagnosis generates a closed curve which precisely reproduces the shape of the indwelled stent and the shape of the inner wall of the biological tissue at the indwelling position of the stent. The optical imaging apparatus analyzes intensity change in transmission direction of the light from the transmission and reception unit for every one of the respective line data; based on the result of the analysis detects pixel data expressing the stent position in the transmission direction; labels each pixel data expressing the detected stent position; eliminates, within the respective labeling groups applied with the same labels, labeling groups in each of which the number of pixel data in the circumferential direction is a predetermined value or less; calculates center position for each labeling group not eliminated; and generates a stent closed-curve using the center position of each labeling group.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/036,468 filed on Sep. 25, 2013, which is a continuationapplication of International Application No. PCT/JP2012/001194 filed onFeb. 22, 2012, and claims priority to Japanese Application No.2011-068628 filed on Mar. 25, 2011 and Japanese Application No.2011-078551 filed on Mar. 31, 2011, the entire content of all four ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to an optical imaging apparatusfor diagnosis and an image processing method.

BACKGROUND DISCUSSION

In the past, there have been used an optical coherent tomography (OCT)apparatus (see, for example, Japanese Application Publication No.2010-14501) and an optical frequency domain imaging (OFDI) apparatusutilizing wavelength sweep, which is an improved type of opticalcoherent tomography apparatus, for a result confirmation after operationat the time of treatment inside a blood vessel depending on a highfunctional catheter such as a stent and the like. Hereinafter, in thepresent specification, the optical coherent tomography (OCT) apparatusand the optical frequency domain imaging (OFDI) apparatus utilizingwavelength sweep will be generically referred to as “optical imagingapparatus for diagnosis”.

Specifically, these apparatus are utilized for specifying the positionof a stent indwelled inside a body lumen (for example, inside a bloodvessel) and the position of a biological tissue from an imagedtomographic image and for confirming an arrangement the stent takes withrespect to the inner wall of the biological tissue.

Here, the stent is generally made of a metal through which the lightcannot penetrate and is mesh-shaped. For this reason, the lightilluminated from an optical probe is mostly reflected at the stentportion and does not reach the inner wall of the biological tissue, andso a situation arises in which only the light passing through apertureportions of the mesh will reach the inner wall. In consideration of suchfact, in case of the tomographic image which is imaged by using anoptical imaging apparatus for diagnosis, the stent and the inner wallwill be respectively displayed as line segments which are discontinuousin the circumferential direction.

However, in a case in which the stent and the inner wall of thebiological tissue are displayed as discontinuous line-segments, itbecomes difficult for a user to comprehend the positional relationshipbetween the stent and the inner wall, for example, to comprehend whetheror not the stent is contacting the inner wall, whether or not the stentis spaced apart from the inner wall, or the like. Consequently, in anoptical imaging apparatus for diagnosis, there is proposed aconfiguration in which a user can visually-comprehend the positionalrelationship between the stent and the inner wall, for example, bygenerating closed curves connecting the discontinuous line-segments(stent closed-curve and inner-wall closed-curve) and by displaying themby superimposing them on the tomographic image (for example, see U.S.Application Publication No. 2010/0094127.

However, in case of U.S. Application Publication No. 2010/0094127, thereis not employed a construction in which noises in the region other thanthe stent and the inner wall are adequately removed, so that thegeneration of the closed curve will be carried out in a state in whichnoises of regions other than the stent and the inner wall are included.As a result, it can be assumed that the stent closed-curve and theinner-wall closed-curve, which are generated, will have shapes lackingin smoothness.

On the other hand, as mentioned above, because the stent is made ofmetal and has a certain amount of rigidity, there seldom happens asituation in which there occurs deformation accompanied by finely spacedconcavity and convexity (precipitous concavity and convexity) in thecircumferential direction with respect to the circular cross-sectionalshape, and it is general that the stent becomes deformed to have agradual curved-shape. In addition, also the inner wall of the biologicaltissue becomes deformed to have a gradual curved-shape in thecircumferential direction with respect to the circular cross-sectionalshape.

In consideration of such fact, it can be said, with regard to the closedcurves of the stent and the inner wall of the biological tissue, thatthe fact of generating a more smooth shape precisely-reproduces theactual phenomenon inside the biological tissue (for example, bloodvessel). Then, in order to reproduce such a closed curve, it becomesindispensable to exclude noises in the regions other than the stent andthe inner wall as much as possible when generating the closed curve andto preliminarily-reduce the number of calculation points (number ofstent candidate-points, number of inner-wall candidate-points) which areused for the generation of the closed curve.

However, when reducing the number of the calculation points too much, itis not possible to precisely-reproduce the cross-sectional shapes of theoriginal stent and inner wall, and there is a possibility that thereoccurs a situation in which there are obtained shapes different from thecross-sectional shapes of the actual stent and inner wall. Inconsideration of such fact, it is desirable for the optical imagingapparatus for diagnosis to have a constitution in which the noises inthe regions other than the stent and the inner wall are discriminatedclearly from those of the stent and the inner wall, and in which theaforesaid noises can be removed reliably when generating the closedcurves of the stent and the inner wall.

SUMMARY

The optical imaging apparatus for diagnosis disclosed here generatesclosed curves which relatively precisely-reproduce the shape of theindwelled stent and the shape of the inner wall of the biological tissueat the indwelling position of the aforesaid stent.

The optical imaging apparatus for diagnosis obtains reflection lightfrom a biological tissue by moving a transmission and reception unitthat carries out optical transmission and reception continuously towardaxial direction while rotating the unit in circumferential direction inthe inside of a body lumen, and which constructs a tomographic image ofthe biological tissue by using line data of interference light that isobtained by making the obtained reflection light and a reference lightinterfere with each other. The optical imaging apparatus includes afirst analysis means for reading-out line data used for construction ofa predetermined tomographic image and for analyzing intensity change intransmission direction of the light from the transmission and receptionunit for every one of the respective line data, a first detection means,based on the analysis result by the first analysis means, for detectingpixel data expressing stent position in the transmission direction forevery one of the respective line data, a first labeling means forlabeling each pixel data expressing the stent position detected forevery one of the respective line data based on each positionalinformation, a first elimination means for eliminating, within therespective labeling groups applied with the same labels by the firstlabeling means, labeling groups in which the number of pixel data incircumferential direction, which is included in one labeling group, is apredetermined value or less, a first calculation means for calculatingcenter position with regard to each labeling group, which was noteliminated by the first elimination means, based on positionalinformation of each pixel data, and a first generation means forgenerating a stent closed-curve by using the center position of the eachlabeling group, which was calculated by the first calculation means.

According to the apparatus disclosed here, it becomes a situation inwhich it is possible, in the optical imaging apparatus for diagnosis, togenerate closed curves which precisely-reproduce the shape of theindwelled stent and the shape of the inner wall of the biological tissueat the indwelling position of the aforesaid stent.

Other features and aspects of the optical imaging apparatus will becomemore apparent from the following explanation with reference to theaccompanying drawings. In the accompanying drawings, the same referencenumerals are applied to the same or similar constitutions.

BRIEF DESCRIPTION OF DRAWINGS

The attached drawings are included in the specification, constitute aportion of the disclosure, illustrate embodiments of the apparatus andmethod disclosed here by way of example, and are used for explainingprinciples of the apparatus and method disclosed here, together with thedescription.

FIG. 1 is a perspective view of the outward-appearance of an opticalimaging apparatus for diagnosis according to one embodiment disclosedhere by way of example.

FIG. 2 is a diagram showing a functional constitution of an opticalimaging apparatus for diagnosis.

FIG. 3 is a diagram showing a functional constitution of a signalprocessing unit.

FIG. 4 is a diagram showing a data structure of a generated tomographicimage.

FIG. 5 is a flowchart showing a flow of a closed-curve generationprocess.

FIG. 6A is a diagram explaining a general outline of a detection processof a stent candidate-point.

FIG. 6B is a diagram for explaining a general outline of a detectionprocess of an inner-wall candidate-point.

FIG. 7 is a diagram explaining a general outline of a labeling processfor stent candidate-points.

FIG. 8 is a diagram for explaining a general outline of an eliminationprocess of a labeling group having stent candidate-points.

FIG. 9 is a diagram for explaining a general outline of an extractionprocess of a representative point in a labeling group having stentcandidate-points.

FIG. 10 is a diagram for explaining a general outline of a labelingprocess for inner-wall candidate-points.

FIG. 11 is a diagram for explaining a general outline of an eliminationprocess of a labeling group having inner-wall candidate-points.

FIG. 12 is a diagram for explaining a general outline of an extractionprocess of a representative point in a labeling group having inner-wallcandidate-points.

FIG. 13 is a diagram showing a stent closed-curve and an inner-wallclosed-curve that have been generated and displayed.

FIG. 14 is a diagram showing a functional constitution of a signalprocessing unit.

FIG. 15 is a flowchart showing a flow of a display process ofstent-thickness.

FIG. 16 is a diagram for explaining a general outline of an additionprocess of stent-thickness.

FIG. 17 is a diagram showing an embodiment of a display process ofstent-thickness.

FIG. 18 is a diagram showing another embodiment of a display process ofstent-thickness.

FIG. 19 is a diagram showing another embodiment of a display process ofstent-thickness.

DETAILED DESCRIPTION

Hereinafter, respective embodiments of the apparatus and methodrepresenting examples of the apparatus and method disclosed here will beexplained with reference to the attached drawings. The invention is notlimited by the embodiments described below and shown in the drawingfigures as various changes and alternations can be introduced andutilized.

First, there will be explained a general outline of an optical imagingapparatus for diagnosis relating to each embodiment disclosed here. Foreach embodiment of an optical imaging apparatus disclosed here, on anoccasion of generating a stent closed-curve, stent candidate-points areextracted from respective line data constituting a tomographic image andthereafter, the extracted respective stent candidate-points are appliedfor labeling based on the positional information of the points. Then, aspecific feature is included in an aspect wherein within the labelinggroups for which the same labeling values are labeled, each labelinggroup in which the number of stent candidate-points in thecircumferential direction, which is included in one labeling group, is apredetermined number or less will be excluded from the calculationtarget of the closed curve, representative points are extracted withregard to respective remaining labeling groups, and the closed curve isgenerated by using the aforesaid extracted representative points.

The fact that there is employed a constitution or configuration in whicheach labeling group, wherein the number of the stent candidate-points inthe circumferential direction is a predetermined number or less, isexcluded from the calculation target in this manner, is caused by thecharacteristics such as shown as follows which are specific in case ofmeasuring the stent by using an optical imaging apparatus for diagnosis.

More specifically, the stent is made of metal, so that in the case ofdirecting light to the stent, the intensity of the reflection light fromthe stent becomes very high compared with the intensity of thereflection light from the regions other than the stent. Therefore, for atomographic image generated from the inside of the stent by a radialscan, the stent will be reproduced as a discontinuous line-segmenthaving a circular shape without any defect. At that time, eachline-segment is formed in the circumferential direction with a lengthequivalent to the thickness of the stent-mesh (for each line-segment,there never occurs a phenomenon in which a lack occurs for a portionthereof and fluctuation occurs for the length of the line-segment).

On the other hand, any noise from other portions than from the stent isdisplayed on an arbitrary position of the tomographic image, but thereseldom happens a situation in which the noise is formed by a lengthequivalent to the thickness of the stent-mesh and at the same time,there are also few chances for the noise to be formed in thecircumferential direction.

Therefore, on an occasion of discriminating the stent from a noise, itbecomes possible to discriminate the stent clearly if assuming that adiscrimination condition is set up according to the fact that there isdisplayed a line-segment having a length corresponding to the thicknessof the mesh and also, according to the fact that the length of theline-segment is continuous along the circumferential direction.

In consideration of such fact, there is employed a constitution orconfiguration, in an optical imaging apparatus for diagnosis relating toeach embodiment described below as examples of the imaging apparatusdisclosed here, in which it is judged that a stent was hit (stent ispresent) in a case in which the number of stent candidate-pointsincluded in one labeling group is a predetermined number or more in thecircumferential direction and it is judged that noise was hit (stent isnot present) in a case in which the number of stent candidate-points isless than the predetermined number.

On the other hand, on an occasion of generating an inner-wallclosed-curve of a biological tissue, a position, that is lowered as muchas a certain amount from the position at which the intensity change ofthe reflection light becomes maximum in the transmission direction(referred to also as radial direction) of the measurement light for therespective line data constituting the tomographic image, is extracted asan inner-wall candidate-point, and each extracted inner-wallcandidate-point is labeled based on the positional information of thepoint. Then, there is a feature that with regard to the labeling groups,within the labeling groups for which the same labeling values arelabeled, in which the fluctuation, in the radial direction for theinner-wall candidate-points included in one labeling group, is a certainvalue or more, the labeling groups are excluded from the calculationtarget of the closed curve and with regard to the respective remaininglabeling groups, representative points are extracted and the closedcurve is generated by using such extracted representative points.

In this manner, there is employed a constitution or configuration inwhich there is extracted a position, which is lowered as much as acertain amount from the position at which the intensity change of thereflection light becomes maximum in the radial direction for therespective line data, as an inner-wall candidate-point and also there isemployed a constitution or configuration in which with regard to thelabeling groups in each of which the fluctuation in the radial directionfor the inner-wall candidate-points has a certain value or more, thelabeling groups are excluded from the calculation target, and this factabove is caused by the characteristics such as shown as follows whichare specific in case of measuring the inner wall positioned at theoutside of the stent by using an optical imaging apparatus fordiagnosis.

More specifically, in a case in which the stent is indwelled in theinside of the biological tissue, the light reaching the inner wall isonly the light which passed through the aperture portion of thestent-mesh. For this reason, while the inner wall is expressed anddisplayed by discontinuous line-segments on the tomographic imagesimilar to the stent, there occurs fluctuation in the lengths of theline-segments (that is, such as the stent, it is not possible to carryout the discrimination thereof depending on the length of theline-segment in the circumferential direction).

On the other hand, the light which reaches the inner wall is nottotal-reflected by the inner wall and reaches a certain depth amount, sothat a situation arises in which the intensity of the reflection lightof the line data increases rapidly at the inner-wall position andmaintains a high level as far as certain amount of depth (that is, it ispossible to reliably-detect the position at which the reflection-lightintensity of the line data becomes maximum and also, fluctuation of thepositions in the radial direction in that case is also relativelylittle).

In consideration of such fact, in an optical imaging apparatus fordiagnosis relating to each embodiment described below as examples of theimaging apparatus disclosed here, a position at which thereflection-light intensity of the line data is lowered from the maximumvalue by a certain amount is made an inner-wall candidate-point. Then,there is employed a constitution or configuration in which it is judgedthat an inner wall was hit in a case in which the fluctuation, in theradial direction for the inner-wall candidate-points included in onelabeling group, is a predetermined value or less and it is judged that anoise was hit in a case in which the fluctuation is larger than thepredetermined value.

Set forth next is a description of respective embodiments of the opticalimaging apparatus and method disclosed here.

First Embodiment 1. Outward-Appearance Constitution of Optical ImagingApparatus for Diagnosis

FIG. 1 is a perspective view of an optical imaging diagnostic apparatus(optical coherent tomography apparatus or optical frequency domainimaging apparatus utilizing wavelength sweep) 100 according to anembodiment representing one example of the optical imaging apparatus andmethod disclosed here.

As shown in FIG. 1, the optical imaging diagnostic apparatus 100 isprovided with an optical probe unit 101, a scanner & pull-back unit 102and an operation control apparatus 103, and the scanner & pull-back unit102 and the operation control apparatus 103 are connected by a signalline 104.

The optical probe unit 101 is inserted directly inside a body lumen of ablood vessel or the like and transmits the transmitted measurement lightcontinuously toward the biological tissue and concurrently, is insertedwith an imaging core which is provided, at the distal end of the imagingcore, with a transmission and receiving unit for receiving the reflectedlight from the biological tissue continuously, and a state of thebiological tissue is measured by using the imaging core.

The scanner & pull-back unit 102 is constituted or configured such thatthe optical probe unit 101 is attached to the scanner & pull-back unit102 in a detachable manner and realizes or undergoes a radial scan(operation in the axial direction and operation in the rotationdirection inside the body lumen) of the imaging core inserted in theoptical probe unit 101 by the driving operation of the an installedmotor. Also, a reflected light received by the transmitting andreceiving unit is obtained and concurrently, the obtained reflectedlight is transmitted to the operation control apparatus 103 through thesignal line 104.

The operation control apparatus 103 is configured to permit input ofvarious kinds of set values on an occasion of measurement and to displaythe measurement result as tomographic images of the biological tissue.

In the operation control apparatus 103, the reference numeral 111indicates a main body control unit. Coherent light data are generated bycausing the reflected light obtained by the measurement and thereference light obtained by separating the measurement light interferewith each other and concurrently, multiple tomographic images areconstructed in the axial direction inside the body lumen by processingthe line data generated based on the coherent light data.

The operation control apparatus 103 also includes a printer & DVDrecorder 111-1, so that the processed result in the main body controlunit 111 can be printed while also being stored as data signals. Theoperation control apparatus 103 additionally includes an operation panel112, allowing a user to input various kinds of set values andinstructions through the operation panel 112, and an LCD monitor 113serving as a display apparatus which displays a plurality of tomographicimages of the biological tissue, which are constructed in the main bodycontrol unit 111.

2. Functional Constitution of Optical Imaging Apparatus for Diagnosis

Next, there will be explained a functional constitution or configurationof the optical imaging apparatus for diagnosis 100. As mentioned above,the optical imaging apparatus for diagnosis can be an optical coherenttomography apparatus (OCT) and an optical frequency domain imaging(OFDI) apparatus utilizing wavelength sweep. The description whichfollows explains, by way of example, an optical frequency domain imaging(OFDI) apparatus utilizing wavelength sweep.

FIG. 2 shows a functional constitution or configuration of the opticalcoherent tomography apparatus utilizing wavelength sweep representingone example of an optical imaging apparatus for diagnosis 100. Thereference numeral 208 indicates a wavelength-swept light source and aSwept Laser is used. The wavelength-swept light source 208 using theSwept Laser is one kind of an Extended-cavity Laser which is composed ofan optical fiber 216 connected with a SOA (semiconductor opticalamplifier) 215 having a ring shape and a polygon scanning filter (208b).

The light outputted from the SOA 215 proceeds inside the optical fiber216 and enters in the polygon scanning filter 208 b and the wavelengthselected here is amplified by the SOA 215 and finally, it is outputtedfrom a coupler 214.

In the polygon scanning filter 208 b, the wavelength is selecteddepending on the combination of a diffraction lattice 212 forlight-splitting the light and a polygon mirror 209. Specifically, thelight which is light-split by the diffraction lattice 212 is focused onthe surface of the polygon mirror 209 depending on two pieces of lenses(210, 211). Thus, it happens that only the light of the wavelengthperpendicular to the polygon mirror 209 returns to the same optical pathand is outputted from the polygon scanning filter 208 b. Consequently,it is possible to carry out the time sweep of the wavelength by rotatingthe polygon mirror 209.

For the polygon mirror 209, for example, a dotriacontahedron mirror isused and the rotation speed thereof is around 50000 rpm. Owing to thewavelength sweep system in which the polygon mirror 209 and thediffraction lattice 212 are combined, it is possible to employ a highspeed and high power wavelength sweep.

The light of the wavelength swept light source 208, which is outputtedfrom a coupler 214, enters one end of a first single mode fiber 230 andis transmitted to the distal end side. The first single mode fiber 230is optically connected with a second single mode fiber 237 and a thirdsingle mode fiber 231 in a photo coupler unit 234 positioned along thelength of the first single mode fiber 230. Therefore, light entering thefirst single mode fiber 230 is transmitted by being split into threeoptical paths at the maximum by this photo coupler unit 234.

On the distal end side ahead the photo coupler unit 234 of the firstsingle mode fiber 230, there is provided, in the scanner & pullback unit102, an optical rotary joint (optical coupling portion) 203 whichconnects between a non-rotary portion (fixed portion) and a rotaryportion (rotational drive unit) and which transmits the light.

Further, on the distal end side of a fourth single mode fiber 235 in theinside of the optical rotary joint (optical coupling portion) 203, thereis connected a fifth single mode fiber 236 of the optical probe unit 101in a freely detachable manner through an adapter 202. Consequently, thelight from the wavelength swept light source 208 is transmitted to thefifth single mode fiber 236 which is passed-through the imaging core 201and which is rotary-drivable.

The transmitted light is illuminated from a distal end side of theimaging core 201 with respect to the biological tissue while beingradially operated (rotated). Then, a portion of the reflected lightwhich is scattered on the surface of or in the inside of the biologicaltissue is taken-in by the imaging core 201 and returns to the firstsingle mode fiber 230 side through the reverse optical path. Further,the light is light-received by a photo detector (for example, photodiode 219) after a portion of the light moves to the second single modefiber 237 side by the photo coupler unit 234 and is emitted from one endof the second single mode fiber 237.

The rotational drive unit side of the optical rotary joint 203 isrotationally driven by a radial scanning motor 205 of the rotary driveapparatus 204. Also, the rotary angle of the radial scanning motor 205is detected by an encoder unit 206. Further, the scanner & pull-backunit 102 is provided with a linear drive apparatus 207 which producesthe axial-direction operation of the imaging core 201 based on aninstruction from a signal processing unit 223.

On the other hand, there is provided a variable mechanism 225 of theoptical path length for fine-adjusting the optical path length of thereference light at a distal end on the opposite side with respect to thephoto coupler unit 234 of the third single mode fiber 231.

This variable mechanism 225 of the optical path length is provided withan optical path length changing means for changing the optical pathlength which corresponds to the fluctuation of the length of the opticalpath such that the fluctuation of the length of the individual opticalprobe unit 101 can be absorbed in the case of the optical probe unit 101being exchanged with a another optical probe unit 101.

The third single mode fiber 231 and a collimating lens 226 are providedon a one-axis stage 232 which is freely movable in the optical axisdirection of the one-axis stage 232 as shown by an arrow 233, and theyform an optical path length changing means.

Specifically, in case of exchanging the optical probe unit 101, theone-axis stage 232 functions as the optical path length changing meanshaving such an amount of variable range of the optical path length,which can absorb the fluctuation of the optical path length of theoptical probe unit 101. Further, the one-axis stage 232 is provided alsowith a function as an adjusting means for adjusting an offset. Forexample, even in a case in which the distal end of the optical probeunit 101 is not closely-attached to the surface of the biologicaltissue, it is possible, by minutely changing the optical path length bythe one-axis stage, to set it to a state of interference with thereflected light from the surface position of the biological tissue.

The light whose optical path length is fine-adjusted by the variablemechanism 225 of the optical path length is mixed with the lightobtained from the first single mode fiber 230 side by the photo couplerunit 234 which is provided along the third single mode fiber 231 and islight-received by the photo diode 219.

The coherent light which is light-received by the photo diode 219 inthis manner is photoelectrically converted and amplified by an amplifier220 and, thereafter, is inputted to a demodulator 221. In thisdemodulator 221, a demodulation process for extracting only the signalcomponent of the coherent light is carried out and the output of thedemodulator 221 is inputted to an A/D converter 222 as the coherentlight signal.

In the A/D converter 222, the coherent light signal is subjected tosampling, for example, at 180 MHz for 2048 points and digital data(coherent light data) of one line are generated. The reason the samplingfrequency is set at 180 MHz is due to an assumption that about 90% ofthe period of wavelength sweep (12.5 μsec) is to be extracted as digitaldata of 2048 points in case of setting the repetition frequency ofwavelength sweep at 40 kHz and it is not limited by this aspect inparticular.

The coherent light data of one line unit, generated in the A/D converter222, are inputted to the signal processing unit 223. In case of ameasurement mode, in the signal processing unit 223, the coherent lightdata are frequency-decomposed by FFT (Fast Fourier Transform) and then,there are generated data in the depth direction (line data), and bycoordinate-converting those data, there is constructed a tomographicimage at each position inside the biological tissue and it is outputtedto an LCD monitor 217 (corresponding to reference numeral 113 of FIG. 1)at a predetermined frame rate.

The signal processing unit 223 is connected further with an optical pathlength adjusting-means control apparatus 218. The signal processing unit223 carries out control of the position of the one-axis stage 232 by theoptical path length adjusting-means control apparatus 218. Also, thesignal processing unit 223 is connected with a motor control circuit 224and receives a video synchronization signal of the motor control circuit224. In the signal processing unit 223, the construction of thetomographic image is carried out in synchronization with the receivedvideo synchronization signal.

In addition, the video synchronization signal of this motor controlcircuit 224 is transmitted also to the rotary drive apparatus 204 andthe rotary drive apparatus 204 outputs a drive signal which is insynchronization with the video synchronization signal.

3. Functional Constitution of Signal Processing Unit

Set forth next with reference to FIG. 3 is a description of thefunctional constitution or configuration of the signal processing unit223 for realizing a construction process of the tomographic image and aclosed-curve generation process based on the line data utilized for theconstruction of the tomographic image in the signal processing unit 223of the imaging apparatus for diagnosis 100. It is possible for theconstruction process and the generation process, which will be explainedhereinafter, to be realized using dedicated hardware and also to berealized by software (by a configuration in which a computer executesprograms).

FIG. 3 is a diagram showing a functional constitution or configurationand a functional block associated therewith for realizing theconstruction process and the generation process in the signal processingunit 223 of the optical imaging apparatus for diagnosis 100.

As shown in FIG. 3, the coherent light data generated in the A/Dconverter 222 is processed in a line data generation unit 301 inside thesignal processing portion 223 such that the number of lines per rotationof the radial scanning motor is 512 by using a signal of the encoderunit 206 of the radial scanning motor 205, which is outputted from themotor control circuit 224.

It is assumed here, as one example, that the tomographic image is to becomposed of 512 lines, but the number of lines is not limited by thisnumber.

The line data 314 outputted from the line data generation unit 301 isstored in the line data memory 302 for every one rotation of the radialscanning motor based on an instruction from the control unit 306. Atthat time, in the control unit 306, a pulse signal 313 outputted from amoving amount detector of the linear drive apparatus 207 is countedbeforehand and thereafter, when storing the line data 314 into the linedata memory 30, the storing is carried out by being correlated with thecount values when the respective line data 314 were generated.

The foregoing description explains that the line data memory 302 isarranged and the line data 314 is stored by correlating the line datawith the count value of the pulse signal 313 outputted from the movingamount detector of the linear drive apparatus 207, but the presentinvention is not limited by this aspect. For example, a constitution orconfiguration is possible in which a tomographic image data memory isarranged behind the tomographic image construction unit 303 and thetomographic image 317 is stored in such a manner as to be correlatedwith the count value of the pulse signal 313 outputted from the movingamount detector of the linear drive apparatus 207.

Referring once again to FIG. 3, based on the instruction from thecontrol unit 306, the line data 315 stored by being correlated with thecount value is subjected to various kinds of processes (lineaddition-averaging process, filtering process and the like) in thetomographic image construction unit 303 and thereafter, is sequentiallyoutputted as tomographic images 317 by being Rθ-converted.

Further, in the image processing unit 305, image processing fordisplaying on the LCD monitor 217 is applied and thereafter, it isoutputted to the LCD monitor 217 as a lateral tomographic image 317′.

Also, the line data 315 stored by being correlated with the count valueis read into the closed-curve generation unit 307 based on theinstruction from the control unit 306, and there is executed a processof generating a closed curve expressing the stent position and a closedcurve expressing the inner-wall position. The generated closed-curve(stent closed-curve, inner-wall closed-curve) data 318 are inputted intothe image processing unit 305 and superimposed with the tomographicimage 317′. Details of the closed-curve generation process in theclosed-curve generation unit 307 will be described later.

In the LCD monitor 217, the tomographic image 317′ processed in theimage processing unit 305 is displayed. Also, in a case in which aclosed-curve generation instruction is inputted by a user through theoperation panel 238, there is displayed a tomographic image 317′superimposed with the closed-curve which is generated in theclosed-curve generation unit 307. The operation panel 238 is an exampleof an input means for inputting information identifying a thickness ofthe stent.

4. Constitution of Tomographic Image Data

Set forth next with reference to FIG. 4 is an explanation of theconstitution or configuration of tomographic image data constructed bythe tomographic image construction unit 303. FIG. 4 illustrates arelationship between a radial operation in the imaging core of theoptical probe unit 101 and the line data constituting the tomographicimage data.

In 4 a of FIG. 4, a reference numeral 401 indicates a cross-section of abiological tissue into which the optical probe unit 101 is inserted. Asdiscussed above, there is attached a transmission and reception unit atthe distal portion of the imaging core 201 which is inserted into theoptical probe unit 101 and this is rotated toward an arrow 402 directionby the radial scanning motor 205.

The transmitting & receiving of the measurement light is carried out byeach rotary angle depending on the transmission and reception unit.Lines 1, 2, . . . , 512 show the transmitting direction of measurementlight at each rotary angle. In this embodiment of the optical imagingapparatus for diagnosis 100, the transmitting & receiving of themeasurement light are carried out intermittently 512 times during thetime when the transmission and reception unit rotates 360 degrees at apredetermined cross-section (predetermined axial position) of abiological tissue 401. The number of times of transmitting & receivingof the measurement light during each 360 degree rotation is not limitedto 512 and it is can be optionally settable.

The portion of FIG. 4 identified as 4 b shows a constitution orconfiguration of line data which are obtained by transmitting &receiving the measurement light at respective rotary angles. As shown in4 b of FIG. 4, the tomographic image data in this exemplified embodimentare constituted by a line data group of 512 lines and each of the linedata is constituted by N-number of pixel data group in the transmissiondirection of the measurement light (N is, for example, 1024).

The transmission & reception of such a measurement light is carried outwhile progressing toward the axial direction inside the body lumen, sothat the line data group shown in 4 b of FIG. 4 is generated by aplurality of sets along the axial direction. Note that the scan(scanning) which repeats the transmission & reception of the signal bythe transmission and reception unit at each of the cross-sections of thebiological tissue in conformity with the progress of the imaging core201 toward the axial direction is referred to generally as “radial scan(radial scanning)”.

5. Flow of Closed-Curve Generation Process

Set forth next with reference to FIG. 5 is an explanation of the flow ofthe closed-curve generation process carried out by the closed-curvegeneration unit 307. When a closed-curve generation instruction isinputted from a user through the operation panel 238, the control unit306 specifies the tomographic image (predetermined tomographic image)which is now displayed on the LCD monitor 217 and, in this situation,instructs the closed-curve generation unit 307 to generate a stentclosed-curve and an inner-wall closed-curve for the tomographic image.

In the closed-curve generation unit 307 which received the closed-curvegeneration instruction from the control unit 306, a closed-curvegeneration process shown in FIG. 5 starts or is initiated.

In step S501, line data corresponding to the tomographic image specifiedby the control unit 306 are read-out from the line data memory 302.

In step S502, high frequency components of the read-out line data areremoved by using a lowpass filter. Since OFDI generally has highresolution, the generated line data include a lot of spectrum noises.Consequently, in this step, the aforesaid spectrum noises are removedand data suitable for the image processing is generated.

In step S503, change of line data in the transmission direction of themeasurement light are analyzed. Specifically, for each of the line data,change of reflection-light intensity in the transmission direction isanalyzed and based on the result of that analysis, there are extracted apixel which becomes a candidate-point of the stent and a pixel whichbecomes a candidate-point of the inner wall. Thus, the closed-curvegeneration unit 307 carrying out the operations in steps S501 and S503is an example of an analysis means for reading-out line data used forconstruction of a predetermined tomographic image and for analyzingintensity change in transmission direction of the light from thetransmission and reception unit for every one of the respective linedata. The closed-curve generation unit 307 is also an example of ananalysis means for reading-out line data used for constructing apredetermined tomographic image and for analyzing maximum intensity inthe transmission direction of light from the transmission and receptionunit for every one of the respective line data. calculation means forcalculating center position with regard to each labeling group, whichwas not eliminated by the first elimination means, based on thepositional information of each pixel data generation means forgenerating a stent closed-curve using the center position of the eachlabeling group, which was calculated by the first calculation means theclosed-curve generation unit 307 carrying out the operations in stepsS501 and S503 is an example of an analysis meanse closed-curvegeneration unit 307 can be a computer (e.g., computer installedsoftware, or hardware for exclusive use) appropriately configured oprogrammed to carry out the operations in steps S501 and S503 (and othersteps as discussed below).

Generally, the stent is made of metal, so that in a case in which thetransmitted measurement light is illuminated onto the stent surface,approximately all of the measurement light which is illuminated onto thestent surface is reflected and it does not reach the rear side of thestent. On the other hand, the biological tissue is constituted by afatty material or the like, so that when the transmitted measurementlight passes through aperture portions of the mesh of the stent formedin a mesh shape and reaches as far as the inner wall of the biologicaltissue, the light penetrates through the tissue by being attenuated inaccordance with a predetermined attenuation rate. More specifically, ina case in which the measurement light reaches as far as the inner wall,it is possible to receive the rear side scattered light in accordancewith the scattering coefficient and the phase function of the biologicaltissue.

Consequently, with regard to the line data generated based on themeasurement light which is illuminated onto the stent surface, thereflection light intensity increases steeply and becomes maximum at theposition corresponding to the stent surface in the transmissiondirection of the measurement light and thereafter, the reflection lightintensity decreases steeply on the rear side from the positioncorresponding to the stent surface.

On the other hand, with regard to the line data generated based on themeasurement light reaching as far as the inner wall of the tissue, thereflection light intensity increases steeply and becomes maximum in thevicinity of the position corresponding to the inner wall in thetransmission direction of the measurement light and thereafter, thereflection light intensity decreases by a constant rate.

In this embodiment disclosed by way of example, by focusing attention onsuch a difference in characteristics between a case in which themeasurement light is illuminated onto the stent surface and a case inwhich the light reaches as far as the inner wall, the stent and theinner wall can be distinguished and the stent candidate-point and theinner-wall candidate-point can be detected depending on the respectivemethods.

Specifically, in step S504, the detection of the aforesaid stentcandidate-point is carried out. FIG. 6A is a diagram for explaining aprocess for detecting a stent candidate-point in step S504. In FIG. 6A,reference numeral 6 a indicates a diagram showing an aspect in whicheach position in the transmission direction of the measurement light(distance from the transmission and reception unit) is arranged on thehorizontal axis and a value of each pixel data of line data (intensityof the interference light) is arranged on the vertical axis, and thereis plotted each pixel data value of the line data generated based on themeasurement light which is illuminated onto the stent surface. Theclosed-curve generation unit 307 carrying out the operation in step S504is an example of a detection means for detecting, based on the analysisresult in step S503, pixel data expressing stent position in thetransmission direction for every one of the respective line data.

As shown in 6 a of FIG. 6A, within each pixel data constituting the linedata, the pixel data at the position on the outside of the cathetersheath (that is, in the diagnosis target region) repeats minimal changein the transmission direction of the measurement light, increasessteeply at the position corresponding to the stent surface andthereafter, decreases steeply. Consequently, in case of calculatingaverage inclination (differential value) in a predetermined length(predetermined length in the transmission direction of the measurementlight) for every predetermined distance in the diagnosis target region,there can be obtained a graph such as shown in 6 b of FIG. 6A.Consequently, by detecting pixel data at the position at which thedifferential value exceeds a predetermined threshold value, it ispossible to detect a stent candidate-point (see 601).

It is possible for the stent candidate-point to be at the position atwhich the differential value exceeds the plus threshold value, to be atthe position at which the differential value exceeds the minus thresholdvalue or to be at the intermediate position between both of them.

Referring once again to FIG. 5, in step S514, detection of theinner-wall candidate-point is carried out. FIG. 6B is a diagram forexplaining a process for detecting an inner-wall candidate-point in stepS514. In FIG. 6B, a reference numeral 6 c indicates a diagram showing anaspect in which each position in the transmission direction of themeasurement light (distance from the transmission and reception unit) isarranged on the horizontal axis and a value of each pixel data of linedata (intensity of the interference light) is arranged on the verticalaxis, and there is plotted each pixel data value of the line datagenerated based on the measurement light which reached the inner wall.

The graph identified as 6 d in FIG. 6B indicates a diagram obtained bycarrying out a smoothing-process for the diagram of 6 c. As shown in 6 dof FIG. 6B, within each pixel data constituting the line data, the pixeldata at the position on the outside of the catheter sheath (that is, inthe diagnosis target region) repeats minimal change in the transmissiondirection of the measurement light, increases steeply in the vicinity ofthe position corresponding to the inner wall surface, becoming a maximumintensity and thereafter, decreases at a constant rate. Consequently, inthe diagnosis target region, it is possible, for the first pixel data atthe position intersecting with the intensity which is obtained bysubtracting as much as a predetermined intensity value, to be detectedas an inner-wall candidate-point (see 611). As indicated by 611 in FIG.6B, the first pixel data at the position intersecting with the intensitywhich is obtained by subtracting a predetermined intensity value fromthe maximum intensity value, is detected as an inner-wallcandidate-point. The side of 611 in FIG. 6B is referred to as thenear-side.

When stent candidate-points are detected in step S504, after step S505,a stent closed-curve is going to be generated by using the detectedstent candidate-points. Similarly, when inner-wall candidate-points aredetected in step S514, after step S515, an inner-wall closed-curve isgoing to be generated by using the detected inner-wall candidate-points.The closed-curve generation unit 307 carrying out the operation in stepS514 is an example of a detection means for detecting pixel dataexpressing inner-wall position of the biological tissue in thetransmission direction for every one of the respective line data basedon the analysis result by the second analysis means.

First, there will be explained the process for generating a stentclosed-curve by using the stent candidate-points.

In step S505, a labeling process is carried out with respect to pixeldata of a stent candidate-point in each of the detected line data.

Specifically, if the distance from the transmission and reception unitto the stent candidate-point of the line data of the labeling processingtarget lies within a predetermined range with respect to the distancefrom the transmission and reception unit to the stent candidate-point ofthe adjacent line data (line data on a line which is up (or down) by oneline from the line of the labeling processing target), the same label asthat of the stent candidate-point on the adjacent line data is addedthereto.

On the other hand, in a case in which the distance from the transmissionand reception unit to the stent candidate-point of the line data of thelabeling processing target does not lie within the predetermined rangewith respect to the distance from the transmission and reception unit tothe stent candidate-point of the adjacent line data, a different labelfrom that of the adjacent line data is added thereto. The closed-curvegeneration unit 307 carrying out the operation in step S505 is anexample of a labeling means for labeling each pixel data expressing thestent position detected for every one of the respective line data basedon each positional information.

FIG. 7 is a diagram showing an aspect in which the labeling process wascarried out in step S505 with respect to pixel data of a stentcandidate-point in each of the line data detected in step S504.

In FIG. 7, hatched pixel data express pixel data of stentcandidate-points. Also, dotted lines surrounding the peripheries of aplurality of stent candidate-points show the fact that the same labelsare added to the stent candidate-points included in the aforesaid dottedlines. In the example of FIG. 7, there are shown two labeling groups(labeling groups 701, 703) each of which is composed of two stentcandidate-points, one labeling group (labeling group 702) which iscomposed of five stent candidate-points and one labeling group (labelinggroup 704) which is composed of three stent candidate-points.

In step S506, there is eliminated the labeling group in which the numberof stent candidate-points included in each labeling group (the number ofstent candidate-points which are added with the same labels) is apredetermined value or less (equal or less than the length correspondingto the thickness of the stent-mesh) in the circumferential direction.This is because there is a high possibility, for the labeling group inwhich the number of the stent candidate-points in the circumferentialdirection is a predetermined value or less, that noise is being detectederroneously as a stent candidate-point. The closed-curve generation unit307 carrying out the operation in step S506 is an example of anelimination means for eliminating, within respective labeling groupsapplied with the same labels, labeling groups in which the number ofpixel data in the circumferential direction, which is included in onelabeling group, is a predetermined value or less.

FIG. 8 is a diagram showing an aspect, with respect to the respectivelabeling groups shown in FIG. 7, in which there were eliminated thelabeling groups in each of which the number of stent candidate-points inthe circumferential direction, which are added with the same labels, isa predetermined value or less. In the example of FIG. 8, there is shownthe fact that a labeling group 701 and a labeling group 703 areeliminated.

In step S507, a representative point is extracted from each labelinggroup which was not eliminated in step S506. Specifically, for theposition of each stent candidate-point included in each labeling group,a mid-value or average-value of the position of each stentcandidate-point in the transmission direction of the measurement lightand a mid-value or average-value of the position of each stentcandidate-point in the circumferential direction are calculatedrespectively, and these are identified as data of the representativepoint. However, it is also possible for the position of the stentcandidate-point, which presents the mid-value in either one of thetransmission direction and the circumferential direction, to be selectedas the representative point. The closed-curve generation unit 307carrying out the operation in step S507 is an example of a calculationmeans for calculating center position with regard to each labelinggroup, which was not eliminated, based on the positional information ofeach pixel data.

FIG. 9 shows an aspect in which representative points are extracted fromthe labeling groups 702 and 704 which were not eliminated in step S506.In the example of FIG. 9, the labeling group 702 is constituted by pixeldata including five stent candidate-points (pixel data including stentcandidate-points from lines 3 to 7 and pixel data having fluctuation forthree pixels in the measurement light transmission direction).Consequently, a pixel 901 is extracted as the representative point fromthe labeling group 702. Similarly, a pixel 902 is extracted as therepresentative point from the labeling group 704.

In step S508, a stent closed-curve is generated by using therepresentative points extracted in step S507. Thus, the closed-curvegeneration unit 307 carrying out the operation in step S508 is anexample of a generation means for generating a stent closed-curve usingthe center position of the each labeling group, which was calculated bythe closed-curve generation unit 307 in step S507.

In this manner, in the optical imaging apparatus for diagnosis relatingto this embodiment, there is employed a constitution or configurationwherein the case in which the number of the stent candidate-pointsincluded in one labeling group is a predetermined number or less in thecircumferential direction is judged to be noise and is excluded from thecalculation target of the closed curve, and wherein with regard to theremaining respective labeling groups, representative points areextracted and the closed curve is generated using the extractedrepresentative points. As a result, it becomes possible to generate aclosed curve in which the shape of the stent indwelled inside thebiological tissue is reproduced more precisely.

Next, there will be explained the process for generating an inner-wallclosed-curve by using inner-wall candidate-points. In step S515, alabeling process is carried out with respect to pixel data of aninner-wall candidate-point in each line data, which was detected. Theclosed-curve generation unit 307 carrying out the operation in step S515is an example of a labeling means for labeling each pixel dataexpressing the inner-wall position detected for every one of therespective line data based on each positional information.

Specifically, if the distance from the transmission and reception unitto the inner-wall candidate-point of the line data of the labelingprocessing target lies within a predetermined range with respect to thedistance from the transmission and reception unit to the inner-wallcandidate-point of the adjacent line data (line data on a line which isup (or down) by one line from the line of the labeling processingtarget), the same label as that of the inner-wall candidate-point on theadjacent line data is added thereto. However, in a case in which thestent does not exist in the obtained tomographic image, the inner-wallcandidate-point is extracted from all line data and it becomes asituation in which only one label is attached. In order to avoid thissituation, a certain upper limit is provided for the number of lines inthe labeling group beforehand and the same label is added thereto if itis within the upper limit thereof. Also, it is possible for the label tobe added for every line number from the very beginning.

On the other hand, in a case in which the distance from the transmissionand reception unit to the stent candidate-point of the line data of thelabeling processing target does not lie within the predetermined rangewith respect to the distance from the transmission and reception unit tothe stent candidate-point of the adjacent line data or in a case inwhich the number of lines in the same label exceeds the upper limit, adifferent label from that of the adjacent line data is added thereto.

FIG. 10 is a diagram showing an aspect in which the labeling process wascarried out in step S515 with respect to pixel data of an inner-wallcandidate-point in each of the line data detected in step S514.

In FIG. 10, cross-hatched pixel data express or identify pixel data ofinner-wall candidate-points. Also, dotted lines surrounding theperipheries of a plurality of inner-wall candidate-points show the factthat the same labels are added to the inner-wall candidate-pointsincluded in such dotted lines. In an example of FIG. 10, there are shownone labeling group (labeling group 1001) which is composed of twoinner-wall candidate-points and three labeling groups (labeling groups1002 to 1004) each of which is composed of three inner-wallcandidate-points.

In step S516, fluctuation in the transmission direction of themeasurement light for the inner-wall candidate-points (inner-wallcandidate-points to which the same labels are added) which are includedin each labeling group is found-out or determined; the aforesaidfound-out fluctuation is compared with that of the adjacent labelinggroup; and the labeling group on the side in which the fluctuation islarge is eliminated (the term “large” refers to the fluctuation in thedistance from the transmission and reception unit to the inner-wallcandidate-point of the line data of the labeling processing target ineach of the labeling groups ranging or varying widely; for example, thefluctuation of the group 1002 in FIG. 11 is “large” compared to that ofthe group 1001). This is because there is a high possibility, for thelabeling group on the side in which the fluctuation in the transmissiondirection is large, that noises are to be detected erroneously asinner-wall candidate-points. The closed-curve generation unit 307carrying out the operation in step S516 is an example of an eliminationmeans for eliminating a labeling group in which the fluctuation of pixeldata, included in one labeling group within the respective labelinggroups applied with the same labels by the second labeling means, in thetransmission direction is large.

FIG. 11 is a diagram showing an aspect in which the fluctuation in thetransmission direction of the inner-wall candidate-points, for which thesame labels are added with respect to the respective labeling groupsshown in FIG. 10, is found-out or determined; the aforesaid found-outfluctuation is compared with that of the adjacent labeling group; andthe labeling group on the side in which the fluctuation is large waseliminated. In the example of FIG. 11, there is shown the fact that thelabeling group 1002 and the labeling group 1004 are eliminated.

In step S517, a representative point is extracted from each labelinggroup which was not eliminated in step S516. Specifically, for theposition of each inner-wall candidate-point included in each labelinggroup, a mid-value or average-value of the position of each inner-wallcandidate-point in the transmission direction of the measurement lightand a mid-value or average-value of the position of each inner-wallcandidate-point in the circumferential direction are calculatedrespectively, and these are identified as data of the representativepoint. However, it is also possible for the position of the inner-wallcandidate-point, which presents the mid-value in either one of thetransmission direction and the circumferential direction, to be selectedas the representative point. The closed-curve generation unit 307carrying out the operation in step S517 is an example of a calculationmeans for calculating, with regard to each labeling group, which was noteliminated by the closed-curve generation unit 307, center positionbased on positional information of each pixel data.

FIG. 12 shows an aspect in which representative points are extractedfrom the labeling groups 1001 and 1003 which were not eliminated in stepS516. In the example of FIG. 12, the labeling group 1001 is constitutedby pixel data including two inner-wall candidate-points (pixel dataincluding inner-wall candidate-points from lines 1 and 2 and pixel datahaving fluctuation for one pixel in the measurement light transmissiondirection). Consequently, a pixel 1201 is extracted or selected (e.g.,through line addition-averaging) as the representative or candidatepoint from the labeling group 1001. Similarly, a pixel 1202 is extractedas the representative point from the labeling group 1003.

In step S518, an inner-wall closed-curve is generated by using therepresentative points extracted in step S517. The closed-curvegeneration unit 307 carrying out the operation in step S518 is anexample of a generation means for generating a closed-curve of the innerwall by using the center position of each labeling group which wascalculated.

In this manner, in the optical imaging apparatus for diagnosis relatingto this embodiment disclosed by way of example, there is employed aconstitution or configuration wherein the case in which the fluctuationof the inner-wall candidate-points included in one labeling group islarge in the transmission direction is judged as a noise case and isexcluded from the calculation target of the closed curve, and whereinwith regard to the remaining respective labeling groups, representativepoints are to be extracted and the closed curve is to be generated byusing the extracted representative points. As a result thereof, itbecomes possible to generate a closed curve in which the shape of theinner wall is reproduced relatively precisely even in a state in whichthe stent is indwelled inside the biological tissue.

6. Embodiment

Next, according to the closed-curve generation process shown in FIG. 5,there will be explained an embodiment in the case of generating a stentclosed-curve and an inner-wall closed-curve of a biological tissue froma tomographic image.

FIG. 13 is a diagram showing an aspect in which a stent closed-curve andan inner-wall closed-curve are generated and displayed according to theclosed-curve generation process shown in FIG. 5.

In FIG. 13, the image identified as 13 a shows one example of atomographic image used for a closed-curve generation process, and theimage identified as 13 b shows a stent closed-curve which is generatedby applying a stent closed-curve generation process with respect to thetomographic image shown in 13 a. Also, the image identified as 13 cshows an inner-wall closed-curve which is generated by applying aninner-wall closed-curve generation process with respect to thetomographic image shown in 13 a. Further, the image identified as 13 dshows an aspect in which the stent closed-curve shown in 13 b and theinner-wall closed-curve shown in 13 c are displayed by beingsuperimposed.

As shown by the images identified as 13 b and 13 c, according to theclosed-curve generation process relating to this embodiment, it becomespossible, with regard to the stent and the inner wall of the biologicaltissue, to generate the closed curves which reproduce the shapes of thestent and the inner wall of the biological tissue more precisely.

As clear from the explanation above, in the optical imaging apparatusfor diagnosis relating to this embodiment, there is employed aconstitution or configuration which focuses attention on the fact thatthe intensity changes of the line data are different between a case inwhich the measurement light is illuminated on the stent and a case inwhich the measurement light reaches the inner wall of the biologicaltissue, wherein the constitution or configuration carries out processessuitable for the respective detections of the stent and the inner wallof the biological tissue. Thus, it became possible to discriminate thestent and the inner wall more clearly.

Also, there is employed a constitution in which a labeling process iscarried out with respect to the stent candidate-points and theinner-wall candidate-points and in which in light of the characteristicsof the stent candidate-point and the inner-wall candidate-point, alabeling group which is judged to be detected erroneously is eliminatedand after this situation, the closed curve is to be generated. Thus, itbecame possible to generate closed curves which reproduce the shapes ofthe stent and the inner wall precisely.

Second Embodiment

In the above-described first embodiment, there was employed aconfiguration in which the shape of the indwelled stent and the shape ofthe inner wall of the biological tissue at the indwelling position ofthe stent are reproduced more precisely. As a result, it became possibleto comprehend the positional relationship between the stent and theinner wall more accurately.

Here, due to the fact that there exists a certain amount of thicknessfor the actual stent, there is only reproduced the reflection surfacefor the stent displayed on the tomographic image and it is not possibleyet to reproduce the accurate thickness of the stent. For this reason,even in a case in which there exists an observed gap between the stentand the inner-wall on the tomographic image, it is not possible to judgewhether a gap actually exists between the stent and the inner wall ofthe tissue or whether the gap is actually caused by the stent-thickness.

This second embodiment makes it possible to confirm the thickness of theindwelled stent on the tomographic image. Hereinafter, there will beexplained an optical imaging apparatus for diagnosis relating to thissecond embodiment. The following description focuses primarily ondifferences between this second embodiment and the embodiment describedearlier, and features in this second embodiment that are the same as inthe first embodiment are designated by like reference numerals and adetailed description of such features is not repeated.

1. Functional Constitution of Signal Processing Unit

First, there will be explained a functional constitution orconfiguration of a signal processing unit 223 of an optical imagingapparatus for diagnosis 100 relating to this second embodiment. FIG. 14is a diagram showing a functional constitution or configuration of thesignal processing unit 223 for realizing a construction process of atomographic image and a stent-thickness display process based on theline data utilized for the construction of the above-describedtomographic image.

As shown in FIG. 14, interference light data generated in an A/Dconverter 222 is processed, in a line data generation unit 301 insidethe signal processing unit 223, such that the number of lines per onerotation of the radial scanning motor will become 512 by using a signalof an encoder unit 206 of a radial scanning motor 205, which isoutputted from a motor control circuit 224.

It is assumed, as one example here, that the tomographic image is to beconstructed from 512 lines, but the invention here is not limited bythis number of the lines.

Line data 314 outputted from the line data generation unit 301 arestored in a line data memory 302 for every one rotation of the radialscanning motor based on instruction from a control unit 306. At thattime, in the control unit 306, a pulse signal 313 outputted from amoving amount detector of a linear drive apparatus 207 is countedbeforehand and when storing the line data 314 into the line data memory302, the data are stored by being correlated with the count value whengenerating each of the line data 314.

The above description explained that the line data memory 302 isarranged and the line data 314 is stored by correlating it with thecount value of the pulse signal 313 outputted from the moving amountdetector of the linear drive apparatus 207, but the invention is notlimited by this aspect. For example, it is possible that a tomographicimage data memory is arranged behind the tomographic image constructionunit 303 and the tomographic image 317 is stored in such a manner as tobe correlated with the count value of the pulse signal 313 outputtedfrom the moving amount detector of the linear drive apparatus 207.

Referring once again to FIG. 14, based on the instruction from thecontrol unit 306, the line data 315 stored by being correlated with thecount value is subjected to various kinds of processes (lineaddition-averaging process, filtering process and the like) in thetomographic image construction unit 303 and thereafter, is sequentiallyoutputted as tomographic image 317 by being Rθ-converted.

Further, in the image processing unit 305, image processing fordisplaying on the LCD monitor 217 is applied and thereafter, it isoutputted to the LCD monitor 217 as a tomographic image 317′.

Also, the line data 315 stored by being correlated with the count valueis read into a stent-thickness addition processing unit 1407 based onthe instruction from the control unit 306, and there are executed anaddition process of an indicator which expresses the stent-thickness anda generation process of a closed-curve which expresses the inner-wallposition (these are collectively referred to as stent-thickness displayprocess). Line data 315′ added with the indicator are inputted to thetomographic image construction unit 303 and the tomographic image 317 isreconstructed. Also, inner-wall closed-curve data 318 are inputted tothe image processing unit 305 and are superimposed to the reconstructedtomographic image 317. Details of the stent-thickness display process inthe stent-thickness addition processing unit 1407 will be describedlater.

In the LCD monitor 217, the tomographic image 317′ processed in theimage processing unit 305 is displayed. Also, in a case in which astent-thickness display instruction is inputted by a user through theoperation panel 238, there is displayed a tomographic image 317′ whichis constructed based on the line data 315′ added with the indicator inthe stent-thickness addition processing unit 1407 and which issuperimposed with the closed-curve.

2. Flow of Stent-Thickness Display Process

Set forth next with reference to FIG. 15 is an explanation of a flow ofthe stent-thickness display process in the stent-thickness additionprocessing unit 1407.

When the stent-thickness display instruction is inputted by the userthrough the operation panel 238, there is carried out, in the controlunit 306, an instruction to generate an indicator indicating thethickness of the stent and an inner-wall closed-curve with respect tothe stent-thickness addition processing unit 1407 in a situation afterspecifying a tomographic image which is displayed on the LCD monitor 217at present.

In the stent-thickness addition processing unit 1407 which received thegeneration instruction of the indicator indicating the stent-thicknessand of the inner-wall closed-curve from the control unit 306, thestent-thickness display process shown in FIG. 15 is started.

In step S1501, information relating to the stent-thickness, which isinputted by the user through the operation panel 238, is set.

In step S1502, line data corresponding to the tomographic image, whichis specified by the control unit 306, are read-out from the line datamemory 302.

In step S1503, high-frequency components of the read-out line data areremoved by using a lowpass filter. Generally, an SS-OCT hashigh-resolution, so that there are included a lot of spectrum noises inthe generated line data. Consequently, in this step, the spectrum noisesare removed and data suitable for the image processing are generated.

In step S1504, changes of line data in the transmission direction of themeasurement light are analyzed. Specifically, in each of the line data,the intensity change of the reflection light in the transmissiondirection is analyzed and based on the analyzed result of the reflectionlight, a pixel which becomes a candidate-point of the stent and a pixelwhich becomes a candidate-point of the inner-wall are extracted.

Generally, the stent is made of metal, so that in a case in which thetransmitted measurement light is illuminated onto the stent surface,approximately all of the measurement light which is illuminated onto thestent surface is reflected and it does not reach the rear side of thestent. On the other hand, the inner-wall is constituted by a fattymaterial or the like, so that when the transmitted measurement lightpasses through aperture portions of the mesh of the stent formed in amesh shape and reaches as far as the inner-wall, the light penetratestherethrough by being attenuated in accordance with a predeterminedattenuation rate. More specifically, in a case in which the measurementlight reaches as far as the inner-wall, it is possible to receive therear side scattered light in accordance with the scattering coefficientand the phase function of the inner-wall.

Consequently, with regard to the line data generated based on themeasurement light which is illuminated onto the stent surface, thereflection light intensity increases steeply and becomes maximum at theposition corresponding to the stent surface in the transmissiondirection of the measurement light and thereafter, it decreases steeplyon the rear side from the position corresponding to the stent surface.

On the other hand, with regard to the line data generated based on themeasurement light reaching as far as the inner-wall, the reflectionlight intensity increases steeply and becomes maximum in the vicinity ofthe position corresponding to the inner-wall in the transmissiondirection of the measurement light and thereafter, it decreases by aconstant rate.

In this embodiment, there will be discussed an example in which byfocusing attention on such a difference in characteristics between acase in which the measurement light is illuminated onto the stentsurface and a case in which the light reaches as far as the inner-wall,the stent and the inner-wall are distinguished and the stentcandidate-point and the inner-wall candidate-point are detecteddepending on the respective methods, but the detection method of thestent candidate-point is not limited by that aspect.

Specifically, in step S1505, the detection of a stent candidate-point iscarried out. The already-described FIG. 6A is a diagram for explainingthe process for detecting a stent candidate-point in step S1505. In FIG.6A, a reference numeral 6 a indicates a diagram showing an aspect inwhich each position in the transmission direction of the measurementlight (distance from the transmission and reception unit) is arranged onthe horizontal axis and a value of each pixel data of line data(intensity of the interference light) is arranged on the vertical axis,and there is plotted each pixel data value of the line data generatedbased on the measurement light which is illuminated onto the stentsurface.

As shown in the reference numeral 6 a of FIG. 6A, within each pixel dataconstituting the line data, the pixel data at the position on theoutside of the catheter sheath (that is, in the diagnosis target region)repeats minimal change in the transmission direction of the measurementlight, increases steeply at the position corresponding to the stentsurface and thereafter, decreases steeply. Consequently, in case ofcalculating average inclination (differential value) in a predeterminedlength (predetermined length in the transmission direction of themeasurement light) for every predetermined distance in the diagnosistarget region, there can be obtained a graph such as shown in areference numeral 6 b of FIG. 6A. Consequently, by detecting pixel dataat the position at which the differential value exceeds a predeterminedthreshold value, it is possible to detect a stent candidate-point (see601).

It is possible for the stent candidate-point to be at the position atwhich the differential value exceeds the plus threshold value, to be atthe position at which the differential value exceeds the minus thresholdvalue or to be at the intermediate position between both the plusthreshold value and the minus threshold value.

On the other hand, in step S1515, the inner-wall candidate-point isdetected. The already-described FIG. 6B is a diagram for explaining aprocess for detecting an inner-wall candidate-point in step S1515. InFIG. 6B, a reference numeral 6 c indicates a diagram showing an aspectin which each position in the transmission direction of the measurementlight (distance from the transmission and reception unit) is arranged onthe horizontal axis and a value of each pixel data of line data(intensity of the interference light) is arranged on the vertical axis,and there is plotted each pixel data value of the line data generatedbased on the measurement light which reached the inner-wall.

The diagram identified as 6 d in FIG. 6B indicates a diagram obtained bycarrying out a smoothing-process for the diagram of 6 c. As shown in thediagram identified as 6 d in FIG. 6B, within each pixel dataconstituting the line data, the pixel data at the position on theoutside of the catheter sheath (that is, in the diagnosis target region)repeats minimal change in the transmission direction of the measurementlight, increases steeply in the vicinity of the position correspondingto the inner-wall surface, becoming a maximum intensity and thereafter,decreases at a constant rate. Consequently, in the diagnosis targetregion, it is possible, for the first pixel data at the positionintersecting with the intensity which is obtained by subtracting as muchas a predetermined intensity value from the maximum intensity value, tobe detected as an inner-wall candidate-point (see 611).

When stent candidate-points are detected in step S1505, after stepsS1506, A1507 and S1508, a process for adding an indicator whichexpresses the stent-thickness is carried out by using the detected stentcandidate-points. On the other hand, when inner-wall candidate-pointsare detected in step S1515, after steps S1516, S1517 and S1518 a processfor generating an inner-wall closed-curve is carried out by using theaforesaid detected inner-wall candidate-points.

First, there will be explained a process for adding an indicator showingthe stent-thickness by using a stent candidate-point.

In step S1506, a labeling process is carried out with respect to pixeldata of a stent candidate-point in each of the detected line data.

Specifically, if the distance from the transmission and reception unitto the stent candidate-point of the line data of the labeling processingtarget lies within a predetermined range with respect to the distancefrom the transmission and reception unit to the stent candidate-point ofthe adjacent line data (line data on a line which is up by one line fromthe line of the labeling processing target), the same label as that ofthe stent candidate-point on the adjacent line data is added thereto.

On the other hand, in a case in which the distance from the transmissionand reception unit to the stent candidate-point of the line data of thelabeling processing target does not lie within the predetermined rangewith respect to the distance from the transmission and reception unit tothe stent candidate-point of the adjacent line data, a different labelfrom that of the adjacent line data is added thereto.

The already-described FIG. 7 is a diagram showing an aspect in which thelabeling process was carried out in step S1506 with respect to pixeldata of a stent candidate-point in each of the line data detected instep S1505.

In FIG. 7, cross-hatched pixel data express pixel data of stentcandidate-points. Also, dotted lines surrounding the peripheries of aplurality of stent candidate-points show that the same labels are addedto the stent candidate-points included in the aforesaid dotted lines. Inthe example of FIG. 7, there are shown two labeling groups (labelinggroups 701, 703) each of which is composed of two stentcandidate-points, one labeling group (labeling group 702) which iscomposed of five stent candidate-points and one labeling group (labelinggroup 704) which is composed of three stent candidate-points.

In step S1507, there is eliminated the labeling group in which thenumber of stent candidate-points included in each labeling group (thenumber of stent candidate-points which are added with the same labels)is a predetermined value or less (equal or less than the lengthcorresponding to the thickness of the stent-mesh) in the circumferentialdirection. This is because there is a high possibility, for the labelinggroup in which the number of the stent candidate-points in thecircumferential direction is a predetermined value or less, that a noiseis to be detected erroneously as a stent candidate-point.

The already-described FIG. 8 is a diagram showing an aspect, withrespect to the respective labeling groups shown in FIG. 7, in whichthere were eliminated the labeling groups in each of which the number ofstent candidate-points in the circumferential direction, which are addedwith the same labels, is a predetermined value or less. In the exampleof FIG. 8, there is shown that a labeling group 701 and a labeling group703 are eliminated.

In step S1508, a representative point is extracted from each labelinggroup which was not eliminated in step S1506. Specifically, for theposition of each stent candidate-point included in each labeling group,a mid-value or average-value of the position of each stentcandidate-point in the transmission direction of the measurement lightand a mid-value or average-value of the position of each stentcandidate-point in the circumferential direction are calculatedrespectively, and these are made to be data of the representative point(that is, the center position is found-out based on the positionalinformation in the transmission direction and the circumferentialdirection of the stent candidate-point and this is made to be therepresentative point).

Further, in step S1509, the data are changed to an indicator indicatingthe stent-thickness, with regard to the pixel data for every number ofpixels corresponding to the set stent-thickness, from the centerposition found in step S1508 toward the transmission direction of themeasurement light.

The already-described FIG. 9 shows an aspect in which representativepoints are extracted from the labeling groups 702 and 704 which were noteliminated in step S1506 and FIG. 16 shows an aspect in which indicatorsindicating the stent-thickness are added with respect to the aforesaidrepresentative points. In the example of FIG. 9, the labeling group 702is constituted by pixel data including five stent candidate-points(pixel data including stent candidate-points from lines 3 to 7 and pixeldata having fluctuation for three pixels in the measurement lighttransmission direction). Consequently, a pixel 901 is extracted as therepresentative point from the labeling group 702. Similarly, a pixel 902is extracted as the representative point from the labeling group 704(see FIG. 9). Then, indicators 1601, 1602 are added with respect to therespective pixels 901, 902 (see FIG. 16).

Next, there will be explained a process for generating an inner-wallclosed-curve by using inner-wall candidate-points. In step S1516, alabeling process is carried out with respect to pixel data of aninner-wall candidate-point in each of the detected line data.

Specifically, if the distance from the transmission and reception unitto the inner-wall candidate-point of the line data of the labelingprocessing target lies within a predetermined range with respect to thedistance from the transmission and reception unit to the inner-wallcandidate-point of the adjacent line data (line data on a line which isup by one line from the line of the labeling processing target), thesame label as that of the inner-wall candidate-point on the adjacentline data is added thereto.

On the other hand, in a case in which the distance from the transmissionand reception unit to the inner-wall candidate-point of the line data ofthe labeling processing target does not lie within the predeterminedrange with respect to the distance from the transmission and receptionunit to the inner-wall candidate-point of the adjacent line data, adifferent label from that of the adjacent line data is added thereto.

The already-described FIG. 10 is a diagram showing an aspect in whichthe labeling process was carried out in step S1516 with respect to pixeldata of an inner-wall candidate-point in each of the line data detectedin step S1515.

In FIG. 10, cross-hatched pixel data express pixel data of inner-wallcandidate-points. Also, dotted lines surrounding the peripheries of aplurality of inner-wall candidate-points show the fact that the samelabels are added to the inner-wall candidate-points included in theaforesaid dotted lines. In an example of FIG. 10, there are shown onelabeling group (labeling group 1001) which is composed of two inner-wallcandidate-points and three labeling groups (labeling groups 1002 to1004) each of which is composed of three inner-wall candidate-points.

In step S1517, fluctuation in the transmission direction of themeasurement light for the inner-wall candidate-points (inner-wallcandidate-points to which the same labels are added) which are includedin each labeling group is found-out or determined; the aforesaidfound-out fluctuation is compared with that of the adjacent labelinggroup each other; and the labeling group on the side in which thefluctuation is large is to be eliminated. This is because there is ahigh possibility, for the labeling group on the side in which thefluctuation in the transmission direction is large, noises are to bedetected erroneously as inner-wall candidate-points.

The already-described FIG. 11 is a diagram showing an aspect in whichthe fluctuation in the transmission direction of the inner-wallcandidate-points, for which the same labels are added with respect tothe respective labeling groups shown in FIG. 10, is found-out; theaforesaid found-out fluctuation is compared with that of the adjacentlabeling group each other; and the labeling group on the side in whichthe fluctuation is large was eliminated. In the example of FIG. 11,there is shown the fact that the labeling group 1002 and the labelinggroup 1004 are eliminated.

In step S1518, a representative point is extracted from each labelinggroup which was not eliminated in step S1517. Specifically, for theposition of each inner-wall candidate-point included in each labelinggroup, a mid-value or average-value of the position of each inner-wallcandidate-point in the transmission direction of the measurement lightand a mid-value or average-value of the position of each inner-wallcandidate-point in the circumferential direction are calculatedrespectively, and these are made to be data of the representative point(that is, the center position is found-out based on the positionalinformation in the transmission direction and the circumferentialdirection of the inner-wall candidate-point and this is made to be therepresentative point).

The already-described FIG. 12 shows an aspect in which representativepoints are extracted from the labeling groups 1001 and 1003 which werenot eliminated in step S1517. In the example of FIG. 12, the labelinggroup 1001 is constituted by pixel data including three inner-wallcandidate-points (pixel data including inner-wall candidate-points fromlines 1 and 2 and pixel data having fluctuation for one pixel in themeasurement light transmission direction). Consequently, a pixel 1201 isextracted as the representative point from the labeling group 1001.Similarly, a pixel 1202 is extracted as the representative point fromthe labeling group 1003.

In step S1519, an inner-wall closed-curve is generated by using therepresentative points extracted in step S1518.

In step S1520, a tomographic image is reconstructed based on the linedata added with the indicator indicating the stent-thickness and bysuperimposing the inner-wall closed-curve thereon, the indicatorindicating the stent-thickness is added thereto and the tomographicimage on which the inner-wall closed-curve is superimposed is displayed.The stent-thickness addition processing unit 1407 carrying out the stepS1520 is an example of a reconstruction means for reconstructing, whenthe stent thickness is inputted, the tomographic image after changingthe pixel data to include the number of pixels corresponding to thethickness of the stent into a display showing the stent toward thetransmission direction from the detected stent position. Thestent-thickness addition processing unit 1407 can be a computer (e.gcomputer installed software, or hardware for exclusive use) programmedor otherwise configured to carry out the step S1520.

3. Embodiment

Next, in accordance with a stent-thickness display process shown in FIG.15, there will be explained an embodiment of a tomographic image inwhich indicators indicating the stent-thickness are added to thetomographic image and the inner-wall closed-curve is superimposedthereon.

FIG. 17 is a diagram showing a tomographic image in which indicatorsindicating the stent-thickness are added and the inner-wall closed-curveis superimposed in accordance with the stent-thickness display processshown in FIG. 15.

In FIG. 17, a reference numeral 1701 expresses indicators indicating thestent-thickness and a reference numeral 1702 expresses the inner-wallclosed-curve. As shown in FIG. 17, the indicators indicating thestent-thickness are extended as much as the stent-thickness radiallyfrom the transmission and reception unit by setting the representativepoints extracted in step S1508 to be the starting points. Thus, itbecomes possible for the user, on the tomographic image, to confirmeasily whether or not the outer surface of the stent contacts theinner-wall and in a case in which the outer surface of the stent isspaced apart from the inner-wall, to confirm rather easily how much thestent is spaced apart from the inner-wall.

As clear from the explanation above, in the optical imaging apparatusfor diagnosis relating to this embodiment, there is employed aconstitution or configuration in which information relating to thestent-thickness is displayed as the indicator on the tomographic imageand concurrently, the inner-wall closed-curve is displayed thereon.

As a result, in the optical imaging apparatus for diagnosis, it ispossible to confirm the thickness of the indwelled stent easily on thetomographic image.

Third Embodiment

In the above-described second embodiment, there was employed, on anoccasion of displaying information relating to the stent-thickness, aconstitution or configuration in which the indicators are arranged inthe radial direction from the representative points of the labelinggroup, which are composed of the stent candidate-points, but theinvention is not limited by this aspect.

For example, it is possible to employ a constitution or configuration inwhich there is generated a stent closed-curve based on therepresentative points of the labeling groups, which are composed ofstent candidate-points; in which there is generated a closed curve whichis a closed curve analogous with respect to the stent closed-curve andwhich is arranged by maintaining a distance equivalent to thestent-thickness with respect to the stent closed-curve; and in whichthey are to be displayed.

FIG. 18 is a diagram showing one example of a case in which thestent-thickness is displayed by a stent closed-curve and a closed curveanalogous to the above-described closed-curve.

In FIG. 18, a reference numeral 1801 indicates a stent closed-curvegenerated based on the representative points extracted in step S1508.Also, a reference numeral 1802 indicates a closed curve which isseparated by a distance (clearance between 1801 and 1802) correspondingto the stent-thickness with respect to the stent closed-curve 1801 andwhich is analogous with respect to the stent closed-curve 1801. Thereference numeral 1702 indicates an inner-wall closed-curve.

In this manner, by generating the closed curves 1801, 1802 and bydisplaying them by being superimposed with the tomographic image, itbecomes possible for a user to comprehend the stent-thickness visuallyon the tomographic image. Also, by displaying the closed curve 1702 ofthe inner-wall together, it becomes possible, on the tomographic image,to confirm rather easily whether or not the outer surface of the stentcontacts the inner-wall and in a case in which the outer surface of thestent is spaced apart from the inner-wall, to confirm rather easily howmuch the stent outer surface is spaced apart from the inner-wall.

Fourth Embodiment

The above-described third embodiment employs a constitution orconfiguration in which the stent-thickness is expressed by two lines ofclosed curves 1801, 1802, but the invention is not limited in thisregard. For example, it is possible to employ a constitution orconfiguration in which the stent-thickness is expressed by painting andfilling the region surrounded (located between) by the two lines of theclosed curves 1801, 1802 depending on a predetermined display format(for example, by a predetermined color).

FIG. 19 is a diagram showing one example in which the stent-thickness isdisplayed by painting and filling the region surrounded by the stentclosed-curve and a closed curve analogous with the aforesaid closedcurve by using a predetermined color.

In FIG. 19, a reference numeral 1801 indicates a stent closed-curvewhich was generated based on the representative points extracted in stepS1508. Also, a reference numeral 1802 indicates a closed curve which isanalogous to the stent closed-curve 1801 and which is arranged withrespect to the stent closed-curve 1801 by being separated with adistance as many as the stent-thickness. Further, a reference numeral1901 indicates a region surrounded by the closed curve 1801 and theclosed curve 1802, in which it shows that the stent exists in theaforesaid region. Reference numeral 1702 indicates an inner-wallclosed-curve.

In this manner, by generating the closed curves 1801, 1802; by paintingand filling the region surrounded by the aforesaid closed curves with apredetermined color; and by displaying the region on the tomographicimage, it becomes possible for a user to visually-comprehend thestent-thickness easily on the tomographic image. Also, by displaying theinner-wall closed-curve together, it becomes possible, on thetomographic image, to confirm easily whether or not the outer surface ofthe stent contacts with the inner-wall and in a case in which the outersurface of the stent is apart from the inner-wall, to confirm easily howmuch degree it is apart therefrom.

The detailed description above describes embodiments of an opticalimaging apparatus for diagnosis and an image processing methodrepresenting examples of the optical imaging apparatus and imageprocessing method disclosed here. The invention is not limited, however,to the precise embodiments and variations described. Various changes,modifications and equivalents can be effected by one skilled in the artwithout departing from the spirit and scope of the invention as definedin the accompanying claims. It is expressly intended that all suchchanges, modifications and equivalents which fall within the scope ofthe claims are embraced by the claims.

What is claimed is:
 1. An optical imaging apparatus for diagnosis whichobtains reflection light from biological tissue of a body lumen bymoving a transmission and reception unit, that carries out opticaltransmission and reception, continuously in an axial direction whilerotating the unit in a circumferential direction inside the body lumen,and which constructs a tomographic image of the biological tissue usingline data of interference light obtained by making the obtainedreflection light and a reference light interfere with each other, theoptical imaging apparatus comprising: first analysis means forreading-out line data used for constructing a predetermined tomographicimage and for analyzing intensity change in transmission direction ofthe light from the transmission and reception unit for every line data;first detection means for detecting, based on the analysis result by thefirst analysis means, pixel data expressing a stent position for everyline data; input means for inputting information identifying a thicknessof the stent; and reconstruction means for reconstructing, when thestent thickness is inputted to the input means, the tomographic image bychanging the pixel data for each of a plurality of the line data toinclude an additional number of pixels in the transmission direction sothat the number of pixels in the pixel data for each of the plurality ofthe line data corresponds to the thickness of the stent in a displayshowing the stent, wherein the first analysis means analyzes theintensity change by finding average inclination of the line data withina predetermined range in the transmission direction for everypredetermined distance, and the first detection means detects pixel datain which the intensity change becomes maximum.
 2. The optical imagingapparatus for diagnosis according to claim 1, wherein the reconstructionmeans further comprises: labeling means for labeling each pixel dataexpressing the stent position detected for every line data based onpositional information of each pixel data; elimination means foreliminating, within respective labeling groups applied with the samelabels in the labeling means, labeling groups in which the number ofpixel data in circumferential direction, which is included in onelabeling group, is a predetermined value or less; calculation means forcalculating a center position of each labeling group, which was noteliminated in the elimination means, based on the positional informationof each pixel data, and wherein the tomographic image is reconstructed,after changing the pixel data for the number of pixels corresponding tothe thickness of the stent, into a display showing the stent toward thetransmission direction from the center position calculated by thecalculation means.
 3. The optical imaging apparatus for diagnosisaccording to claim 1, further comprising: second analysis means forreading-out line data used for a construction of a predeterminedtomographic image and for analyzing maximum intensity in thetransmission direction of light from the transmission and reception unitfor every line data; second detection means for detecting pixel dataexpressing inner-wall position for every line data based on the analysisresult by the second analysis means; labeling means for labeling eachpixel data expressing the inner-wall position detected for every linedata based on positional information of each pixel data; eliminationmeans for eliminating a labeling group in which the variation ofpositional information of pixel data, included in one labeling groupwithin the respective labeling groups applied with the same labels bythe labeling means, in the transmission direction is larger than apredetermined variation; calculation means for calculating, with regardto each labeling group which was not eliminated by the eliminationmeans, center position of the labeling group based on positionalinformation of each pixel data of the labeling group; and generationmeans for generating an inner-wall closed-curve by using the centerposition of each labeling group, which was calculated by the calculationmeans.
 4. An image processing method of an optical imaging apparatus fordiagnosis which obtains reflection light from biological tissue of abody lumen by moving a transmission and reception unit, that carries outoptical transmission and reception, continuously in an axial directionwhile rotating the unit in a circumferential direction inside the bodylumen, and which constructs a tomographic image of the biological tissueusing line data of interference light obtained by making the obtainedreflection light and a reference light interfere with each other, themethod comprising: reading-out line data used for construction of apredetermined tomographic image and for analyzing intensity change intransmission direction of the light from the transmission and receptionunit for every line data; detecting, based on a result of the analyzingof the intensity change, pixel data expressing stent position for everyline data; inputting information relating to thickness of the stent; andreconstructing the tomographic image, when an instruction is inputtedthat the thickness of the stent is to be displayed, by changing thepixel data for each of a plurality of the line data to include anadditional number of pixels in the transmission direction so that thenumber of pixels in the pixel data for each of the plurality of the linedata corresponds to the thickness of the stent in a display showing thestent, wherein the intensity change is analyzed by finding averageinclination of the line data within a predetermined range in thetransmission direction for every predetermined distance, and the pixeldata in which the intensity change becomes maximum is detected.
 5. Theimage processing method of an optical imaging apparatus for diagnosisaccording to claim 4, wherein the reconstruction process furthercomprises: labeling process for labeling each pixel data expressing thestent position detected for every line data based on positionalinformation of each pixel data; elimination process for eliminating,within the respective labeling groups applied with the same labels inthe labeling process, labeling groups in which the number of pixel datain circumferential direction, which is included in one labeling group,is a predetermined value or less; calculation process for calculating acenter position of each labeling group, which was not eliminated in theelimination process, based on positional information of each pixel data;and wherein the tomographic image is reconstructed after changing thepixel data for the number of pixels corresponding to the thickness intoa display showing the stent toward the transmission direction from thecenter position calculated in the calculation process.